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Primary measures to reduce tar formation in fluidised-bed biomass gasifiers: Final report SDE project P1999-012
Kiel, J.H.A.; Paasen, S.V.B. van; Neeft, J.P.A.; Devi, L.; Ptasinski, K.J.; Janssen, F.J.J.G.; Meijer, R.; Berends, R.H.; Temmink, H.M.G.; Brem, G.; Padban, N.; Bramer, E.A.
Published by: Publication date:
ECN 1-3-2004
ECN report number: Document type:
ECN-C--04-014 ECN publication
Number of pages: Full text:
108 Download PDF  

The main objective of the work described in this report has been toadvance the knowledge base on tar formation in air-blown, atmospheric-pressure fluidised-bed gasification of woody biomass, in particular with respect to: ·the effect of various fuel properties and gasifier operating conditions, ·the underlying mechanisms, and ·the impact of the resulting tar concentration and composition on the performance of downstream processes. With respect to the latter, water solubility and condensation behaviour, expressed in terms of the tar dewpoint, were identified as the most important tar properties. The work was focussed mainly on bubbling-fluidised-bed (BFB) gasification, but circulating-fluidised-bed (CFB) gasification was addressed as well. Furthermore, much attention was given to the definition, measurement and classification of tar. In this respect, tar was defined as "all organic compounds with a molecular weight larger than benzene (excluding soot and char)". Measurement of individual tar compounds was conducted using either the Solid Phase Adsorption method or the Guideline method. In an extensive experimental programme, the impact on tar formation of three fuel properties (ash content, moisture content and lignocellulose composition) and three operating conditions (gasification temperature, gas residence time and bed material/additives) was determined in lab-scale bubbling-fluidised-bed gasifiers. The results were found to be representative for circulating-fluidised-bed (CFB)-gasification as well, provided that differences in gasification temperature and gas residence time (distribution) are taken into account. The report contains data to account for these differences. In addition to the experimental work, attempts were made to model tar formation. Subsequently, the advanced knowledge base was applied to assess the practical and economic feasibility of identified, most promising primary measures.

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